There are two styles of cross-country skiing - classical (straight-striding technique) and freestyle (unrestricted skating-like motion).
Cross-country consists of sprint (contested over several rounds rather than a single race) and combined pursuit events.
Men compete in the 1.5 kilometre sprint, 15km and 50km classic, 30km freestyle and the combined pursuit (10km classical and 10km freestyle).
Women take part in the 1.5km sprint, 10km and 30km classical, 15km freestyle and the combined pursuit (5km classical and 5km freestyle).
The biathlon involves cross-country skiing and rifle shooting. There are eight categories - men's and women's sprint, pursuit, individual and relay.
Competitors can ski in any style but must not only complete the distance (from 7.5km to 20km) but also hit five targets with five bullets.
For each target missed in the sprint, pursuit and relay events, athletes ski a lap around a 150-metre penalty loop.
In the individual event, competitors stop four times at the firing range and must hit all five targets with five bullets. For each target missed, one minute is added to their total time.
In the relay, four-person teams ski 7.5km each. Each team member has two firing sequences and is allowed three extra bullets (for a total of eight) to hit five targets.